Question

The deflection of pitch angle between two successive steps (rungs) of DNA is

• A. ${72}^{\circ }$
• B. ${54}^{\circ }$
• C. ${36}^{\circ }$
• D. ${18}^{\circ }$

Answer 1

Answer: (C)

${36}^{\circ }$

The twist of a DNA double helix corresponds to the angular rotation that is needed to get from one base pair to the next. In an idealized DNA molecule the twist is 36 degrees, meaning that if you rotate one base pair by 36 degrees and move it up the helix by 0.34 nm, you will occupy the position of the next base pair. Thus, the distance or rise along the axis of the double helix is 0.34 nm between 2 consecutive base pairs.